Japan's Naomi Osaka said she was “in a state of shock” on Saturday after holding her nerve to battle past Petra Kvitova and win the Australian Open in a three-set thriller that also gives her the world number one ranking.

The fourth seed and US Open champion triumphed 7-6 (7/2), 5-7, 6-4 in a 2hr 27min epic over the Czech eighth seed to claim back-to-back Grand Slams and become the first Asian, male or female, to hold the top spot.

Melbourne Park erupted in thunderous cheers as the Japanese youngster fell to one knee, head bowed, before collecting the trophy from China's Li Na — who lifted the same silverware in 2014 to become the first Asian to win a major.

It was a cathartic moment for 21-year-old Osaka, whose breakthrough Grand Slam win at Flushing Meadows was marred by boos in the wake of losing finalist Serena Williams' tirade at the umpire.

Rather than tearfully hiding her face as she did in New York, Osaka beamed with joy at a win she said was still sinking in.

“I felt like I was in a state of shock through the entire trophy presentation,” the 21-year-old said.

Osaka was reluctant to say how she felt compared to Flushing Meadows but believed she and Kvitova were fairly supported in Melbourne.

“In New York, most of the crowd was for Serena and here it felt like it was split a little bit,” she said.

“Honestly, when I was playing and I heard the crowd was for both of us I was very happy but at the same time I was trying to focus on the match.”

A rattled Osaka almost blew her title hopes with one hand on the trophy when she failed to convert three championship points leading 5-3 in the second set.

The never-say-die Kvitova forced a deciding set before Osaka finally edged ahead with a decisive break early in the third.

“Of course I felt very disappointed and sad when I had three match points,” she said.

“I tried to tell myself there's nothing I can do about it. I had to regroup and told myself I didn't want any regrets.”

Osaka is the youngest woman to win back-to-back majors since Martina Hingis in 1998 and the youngest number one since Caroline Wozniacki in 2010.

'Congrats Champ!'

Her gutsy performance confirms her status as the leading light of tennis' new generation.

“Well, after winning the US Open Naomi Osaka became a star. And now, after winning the Australian Open and becoming world number 1, she is a superstar! Congrats Champ,” 18-time Grand Slam winner Martina Navratilova tweeted.

Kvitova can console herself with a career-best performance at Melbourne Park, where she did not drop a set on her way to the final.

It was her first Grand Slam decider since a burglar slashed her racquet hand in a 2016 knife attack and the Czech has shown she is again a contender at the majors.

“Thank you for sticking with me even when we didn't know if I would able to hold a racquet again,” Kvitova told her team, with her voice cracking.

“It's crazy. I can hardly believe that I just played in a Grand Slam final again.”

The pair had never met before and Osaka initially struggled to unlock the lanky left-hander's serve, while Kvitova at times could not handle her opponent's powerful returns.

The Czech blew three break chances in a crunch sixth game as the first set went to a tie-break, which Osaka ran away with it 7-2, taking the first set the Czech conceded in the entire tournament.

Kvitova regrouped with an early break in the second but Osaka did not panic, immediately breaking back.

The Japanese star broke again to take control as Kvitova's error rate climbed, bringing up three championship points. But the Czech saved all of them.

She then won four straight games to win the set as Osaka left the court with a towel draped over her head.

She regained her cool and clipped a clean backhand winner to take a break point in the third game of the decider and was up to the task when Kvitova forced her to serve for the match.